Electrical musical instrument



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Feb. 6, 1951 J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT 4 Sheets-Sheet 2 SQ) vi) IIIIIUI'III Mme/2 for (fa/20 Aggie/2w? Filed May 5, 1945 J- M. HANERT ELECTRICAL MUSICAL INSTRUMENT Feb. 6, 1951 Feb. 6, 1951 J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT 4 Sheets-Sheet 4 Filed May 5, 1945 Md 1 P. n n

a H WM w M J Patented Feb. 6, 1951 UNITED STAT EST PATENT ICE 2,540,727 E'I'JEU'I RICALMiTS'ICALJfiSTRUMENT J'ohnM' Haters Fan: Ridge; 111 ass-em to Hammonu msti-ument Company, Chicago; 111;;- enumeration-'01- nelaware Application May1945, Serial No. 592,098

16 Claims.

or My invention relates generally to electrical musical instruments'and more particularly to improvements in the toneg'en'erating and con-- trolling apparatus ofme1ody' type instruments; In some types ofmelody instruments; that is,

instruments "which produce but one tone ate time; there nasbeen employed a, master'oscillater supplying signals to a series of 'ca'scade'dfrequency'dividers; such as shown; for exampm; in my" copending'application; semi No. 519,838; filed January. 27, 1944, and since'aba'ndon'ed. The" masteroscillator hars'customarily beenjof the inductance-capacitancetuned type. Inthis meth odof tuning an'oscillatorit becomes a"matter"of considerable expense to" provide the necessary large "number'of capacitors which must be care fullyiselectedand" some ofwh'ich must be very" apparatus for changing thefre'quencyf of awien bridge oscillator to'fa preselected frequency by successively changing the effective impedances in the circuits ofthe "oscillator. 7 v

A'" further' object isto" provide a master" oscil lator tuning system which "is tuned by thed'e 0 pression of playing keys, and in which the tuning circuits arearran'ged such that when the ner the 'os'cil1ator wi11 generates frequency in termediate the ir equencies -to-which it is tuned b-y the two keys, as an incident to changing to the frequency of the last depressed key.

A furtherobject is to provide" frequencygeneratingapparatus for a, musical-instrument ofthe melody-type iii-which relatively smooth glissando effects may be obtained.

A further-object'is to-pr'ovide a secondary' tun: ing circuit for smoothly and dependablyobtain ing a quartr tone scale with bu't twelve" keys to the octave.

Another object is to provide akeyboard musical-instrument of-the melody type in which simultaneousdepression-of two'- adjacent keys roduces l a. tonewhcse frequency is related-to oneof the keys but detuned-bya factor'of a quart'er tone;

Aiurtl'ier object" isto provide'a' tuning-mechanism for an oscillator-requiringchanges in two circuits thereof; which will change the impedances in these two= circuits in a predetermined sequencesuc'h that the oscillator does not' stop oscillationhduring the tuning process.

A further' object is t'c provi'd" an improved means for tuning an oscill at'oi 'o type in which-the oscillator does not' stop' o'sc lating as it's frequefr icf is" changed but ifiste shifts gradually from one frequencyto-a'ncith'er -'to which it is being'tu'n'ed;

Other obj ects will appear from" th follow' description, reference bei-n'g had to tlie acc'cmpanying' drawings in which Figs. la, 1b and-1c together-'censtitiite' a;= -Wii' ing diagram;

Fig. 2 is a diagrammaticr'epresentation o 1ie= key operated switches showing their sequence-of operation;

Fig. 3 is a longitudinal-sectional vievifiof the manually operated dynamic volume con'trol switch mechanism; and

Fig. 4is an end elevational viewtherof with a portion of the'casin'g broken'away to "reveal -the operating parts-L- General description The invention may be described generally 'as 'a melody instrument h'a'yiiis a masteroscil-laItor' of a resistance tuned Wie' br dge tyee uch iefexample as is sliown 'in the H'e'WIett -Patei it -Nc 2 ,2wi8,-87-2.- The 4 master oscillator oilfiput 'iSFC pled to a series of' pi ilse -sl1ai"pening pefitedes change the 'gen'erally sinusoidai' o'si-l-lator 'o' put wa ve into 'retanemar-waves iid 'tli ear through a rectifier tr iodet coriye'it'tl'ie reta r gular' waves into sharply peaked unidirectibn 1 pulses; These pulses areimpressed upon' the input-circuits ofth'e fi'rst' of a series ofi alte'rinite pulse responsive frequency divider stages- Sfg nals representingdifferent" music's-1 tona ua ties are derived from different 'pcrt'io s'of the cuit'sof each oftl iese' divider stages' and are lectively' impressed upon the input of a pr amplifier,- the outpfitof wl'iic'h is provided wi a plurality of selectively operable tone 'co'rit' filters. The signals of Y the quality 'thus pie'Se-'-=" lected and predetermined-are supplied tomcatput an'd' power amplifying circuit and tretnsliited into sound.

The Wien bridge oscillatoris tuned by suc cessi'vely changing the effectiveimpedancef or each of its frequency controlling circuits-ina predetermined sequence; In addition the opertion of thekeys under'cert'ain' circumstancesmay cause the oscillator tobe tuned'to the frequency intermediate the adjacent semitone' frequencies so as to make it possible tdplay'aquarter-thine chromatic scale. Furthermore; the operation"- of each of the keys is effective to render t v outputamplifier capable of transmittingthsi nal, the rate of attack and decay of the tone being automatically controlled.

The oscillator is provided with a vibrato mechanism whereby its frequency may be continuously varied through a given range, such as 3%, at a periodicity in the order of 7 C. P. S. In addi-- tion the oscillator tuning means is provided with an optionally operable switch for opening one branch of the tuning circuit when no key is depressed. Through the time delay action of a thermistor impedance element, the approach to the steady state frequency of the oscillator is delayed, to produce an interesting musical effect when playing in a non-legato manner.

Oscillator and tuning means The oscillator comprises a pair of beam power pentodes l and l I, each supplied with plate current from a suitable power supply, indicated as a- +300 v. terminal, through load resistors RM and R15. The screen grids l6 and I! of these pentodes are connected to the +300 v. terminals through voltage dropping resistors Rl8 and R19 and are by-passed to ground through ca-- pacitors C20 and C2! respectively. The grid bias for the pentode I0 is provided by a thermistor 22 connected between its cathode 26 and ground. The cathode 21 of the pentode ll is connected to ground through a self-bias resistor R23. The output of the pentode i0 is coupled to the input of the pentode II through a blocking capacitor C28 connected between the plate 30 of pentode l0 and grid 33 of pentode H. The plate 3| of pentode H is connected, through a relatively large blocking condenser C34 and a degenerative feedback resistor R36, to the cathode 26 of the pentode ID. The plate 3| is also connected to grid 39 through a regenerative circuit including the capacitor C34, a conductor 40, one or more of a plurality of tuning resistors R42, conductor 44, and phase shift capacitor C46 having a parallel tuning capacitor C41. The grid 39-is also connected to ground through a phase shift network comprising a capacitor C50, having a tuning capacitor C52 in parallel therewith, and one or more of a plurality of resistors R54, depending upon which of the playing keys is depressed. The over-all tuning capacitors C41 and C52 preferably have a common operating means. The circuit including the resistors R42, and C46, C41 may be considered as the series feedback circuit, while the circuit including resistors R54, and C50, C52 may be termed the shunt feedback circuit.

.The keyboard for playing the instrument is diagrammatically illustrated as comprising three octaves of keys bearing their customary note designations C to B. Each key operates four switches 60, 6|, 62 and 63. As illustrated in 2, these switches are operated in a predetermined sequence by an actuator 61 which, upon depression of the key, will first cause closing of switch 60 and then switch 6|. The switch 62 may close substantially simultaneously with the switch 66 but the switch 63 should not close until a short time after switches 66, BI and 62 have been closed.

The switch 60, as previously indicated, makes contact with a bus conductor 40, while the switches BI, 62 and 63 respectively make contact with grounded bus bars 64, 65 and 66.

Alternate ones of the movable arms of switches 62' are connected to conductors 68 and 69 respectively. The conductor 68 is connected to the'grid 39 of pentode [0 through a quarter-tone interval tuning capacitor 010 while the conductor 69 is connected to said grid through a second quarter-tone tuning capacitor C1! whose value may be the same as that of the capacitor 016.

A vibrato apparatus is adapted to be connected to the grid 39 of pentode Hi to slightly vary the frequency of oscillation thereof upon closure of a single-pole double-throw switch '12. A vibratory grounded reed 14 is adapted to be maintained in vibration by an eleotromagnet 16 having one end of itswinding connected to a suitable energizing source such as a terminal +50 v. of the power supply system, while its other terminal is connected to a contact 18 which completes a circuit through the winding when the reed is in the upper portion of its oscillatory swing. During approximately one half of the period of oscillation of the reed M it engages a contact which is connected through a tuning capacitor C82 and switch 12 to the grid 39. When the vibrato is not desired, the switch 72 is turned to the off position in which event a capacitor C84 is connected between the grid 39 and ground, the value of the capacitor C84 being approximately one half that of the capacitor C82, thus compensating for the change in median capacity produced when the switch 12 is in its full line position and the vibrato in operation. An antispark resistor R86 is connected between the contact T8 and ground.

The output of the Wien bridge oscillator, comprising the pentodes l6 and II and their associated circuits, is in the form of a sinusoidal wave which may vary somewhat in amplitude during the interval that its frequency is being changed. In order that such transient changes in amplitude shall not be present in the tone signal ultimately produced, the output of the oscillator is transmitted through a series of pentodes 96, 92 which are biased so as to be amplitude limiting and thus convert the sine wave output of the oscillator into equal amplitude substantially vertical front rectangular waves. Since such amplitude limiting tubes and circuits are known, it is believed that no further description of the pentodes 90 and 92 is necessary.

Theoutput circuit of the pentode 92 is coupled to the input circuit of a triode 94 which is biased to operate as a rectifier.

Frequency dividers The output of the rectifier 94 is impressed upon the grids 98, 99 of alternate pulse responsive'frequency divider triodes I60 and II. The triodes I00 and I01 and their associated circuit elements are disclosed in greater detail in my copending applications, Serial Nos. 569,567 and 569,568, filed December 23, 1944. Application No. 569,567 matured into Patent No. 2,514,490 on July 11, 1950. Application No. 569,568 has since become Patent No. 2,468,062, issued April 26, 1949. In general, it may be stated that these triodes I00 and |6| operate to supply a rectangular wave at an output terminal I62 which has a frequency exactly one half that of the input frequency supplied from the rectifier triode 94. The signal appearing at the output terminal I02 is impressed upon the input circuit of a pulse sharpening and rectifying triode 104 which supplies a signal suitable for the operation of the next alternate plus responsive frequency divider stage.

The signal appearing at the terminal I62 is also impressed upon the input circuit of a triode 166 which operates as a rectifier and pulse generator. The pulses appearing in the output'of the anew-mew 'duraticnlethan ithe pulses producedby the .tri'ode I104. Thesecondwthird and. fourth divider stages are generally similaretozthe wfirst divider stage operate. successively to halve-the frequency supplied by the preceding stage. Similar referreheat-characters 'have therefore "been applied to -:the corresponding parts.

.The :signals produced :in these various stages farexadaptedztof be Sselectively transmitted to bus ":barz H upon :closure of one'or more of apluraility toi; switches I12, I Band I M to controlithe .transmissionrofi tone signals JOf theaqualities in- -dicated-vby 'the legends adjacent the switches. ;It-'e.wi'll.be noted that .the switches I I2 controlling "it-hes-transmissionto the bus :bar III! of the tones oflthewoodwind family, namely, tones contain- :ing.zpredominantlyrthe .odd :harmonic series, :are :derivedifrom .the outputof the .triode 1! [iii through --a::suitable=:'mesh comprising resistors Ri I6,..RI.I'7 -and1capacitorsCH9 and CIZB. This .mesh is effectiveto attenuate undesirable high harmonics :as;welli-as'toattenuate the lower order liar-mon- -zicsiand therebyzto producea tone signal oferich :xilarinetelike quality.

iUpon'closure of the switch H3 a signal from the-output of thetriode IE6 is impressed upon rcollector bus I'lfl through a mesh comprising re ;sistors..RI22, R123 .andacapacitor CI26. .This -mesh-:togethcr withxthe plate lo'ad resistor EH28 sandarshunt'capacitor C130 is effective to producea generally sawtooth wave closely simulat- .ing in tone quality the tones of bowed string orchestral instruments. The odd harmonic family present at the terminal H12 is effectively changed due torthe provision of a capacitor C524 of size to 'besubstantiallycurrent limiting with respect ltogrid resistor RIZB at the frequency produced when the-highest key B of the keyboard is. depressed-and due therectifying action of triode 406.

The-zclosure of the switch II I results in supplying thesignal from the output of triode I90 throughla mesh zcomprising resistors Rl32; RI33 and-capacitor ,CI34. The triode I04, due to the .relative values of its current limiting blocking capacitors-CB and grid resistor RIM, :and due to: its rectifying. action, eliminates the odd harmonics present inthe signal appearing at the terminal 1.02, with the'result that the signal appearing at the switch H4 is of exceedingly bright toner quality closely simulating the eiiects ,-of .-.brass instruments such as the trumpet.

Output circuits "The' signals thus supplied to the collector'bus IIU are impressed upon the input circuit of a preamplifier triode M0- through a blocking ca- :pacitor'CI-42. The output of the preamplifier =triode I40 mayha-ve its effective tone quality varied :by means of :a suitable tone controlling *Ifilter I'fl rendered selectively operative by opening one or more switches I46. The signal as thus modifiedsby :one or more of these filters is coupled by a transformer TI' IB to the grids of a pair .of pushepull triodes 150,151. The cathodes I52 ZOfiIthBSBLtIiOdBS are connected toground and coupl'edto the center tap I53 of the secondary :winding ofiltransformer Tldfithrough an attack and :decay :capacitor C154. Normally, the triodes ilEIIand ISI-arebiased beyond cutoff through aresistor RI-EB connected between the center tap I53 and azsuitable :source of biasing potential indicated .assterminal --.50 v. The center tap I53 connected through an attack tresistor BI 58 "is connected to. all :of the playing 'skeysoperated switches '63= and ;.may be 'v'connectedthroug'h any one ofhthese switches tOtthQflfOllIldBd bus E5. 'Whenthus "connected rthe resistors ?R'|56 wand RI 58 act :asa "voltage divider to decreaseathe. :bias :on the" triodes 1'50: and Iii-hat .arate determined byithe capacitor C154 :50 :as "-120 obtain arrelaitively' 'fast (but transientless iattackzwhen a key is depressed, .as well ras a relatively tsiast transientlesssdecay when'the sdepressedikey isreleased. :I'Iriodes I-Efland I5I may be.:of::the 6J5typehav- :ingza relativelyrsharp .cutoiT. The signal applied ,to :their-grids :is, :in general, iioframplitud'e :iust

,suflicient' to wavoidr producing Idistortion. Under these :conditions, "the v:signal ramplitude'i will:;scan rover substantially theventire; linear zportionrof the :grid voltage-plate current characteristic, :andrwill :Lthus be effective :to "modulate the plate current to a very considerable extent andthereby :nii-nimize the transient due to the direct nnmodulated plate current which will occur because-of :the unavoidable'slight dissimilarities in thestwo portions of the push-pul1 transmission. system. Under these conditions, 'theitubes I159 an'dJI'BI will cause .a very considerable :degree of distortion during the attack and decay portions of theiitone signals,'but inasmuch .as these portions :;of "the "signals "occopy a -verysrsinill period of time the summation and-difference distortion terms resulting from the non-linearity ofctheagrid. voltageeplate current characteristics are :nottp'erceptible ito'lthe ear, and the overall result'aisithat of-aatransientless attack and .decay. Thisihas the advantage that the exact similarity .of theitwoisides-of :the push-pull system "are not :of great importance. The similarity. of the 'twotsides ;of.lth'e. push-pull system are made practically/identical:insofar..as the plate loading is concernediiby using an output transformer T162 in which the; number of turns between-xthezcenter tap (which is connected to the high voltage terminal indicated as +300 v.) and the extremities are kept equal. This equality 'isrrela'tively. easyto maintain, since the commercial tolerance on the number .of turns on a transformer mayibelzh'eld to :a part in several thousand.

The secondary Winding of transformer TIEZ is coupled .tothe :input circuits of remote cutoff pentodes I64, I65. A volume adjusting resistor RIBBis -connected:sbetween the control :grids of pento'des I64 and IE5. The -centertap IB'I of the secondary 20f transformer3TI62 is connected .to a bus "conductor IG8 througha decouplingresister-R and is connected togroun'd through a time constantcapacitor CH2. The conductor IE8 is connected toxground through a voltage dividing resistorizRlfl l. Asource of negative biasing svoltage,iindicated as a terminal -50 v., is normally connectedto the conductor Hi8 through a plurality of resistors RI IE or logarithmically graded values such Ithatsuccessive opening of these switches will causethe output of pento'des I64, 65 to increase in equal db steps -of 'approximately v2 db.

Asshown in Figs."3 .aand 4 this dynamic volume control includes the-resistors 'RI'IB, which are adapted to be successively disconnected and connected to the-conductor I68 upon manual operationof a key I86. The key Hill is mounted on a pair of channels 1 81 which are-secured to-leaf springs lat-by brackets-I83. Secured to one of the channels I8! isanractuatorl88of"insu ating material, which is adapted, as thekey I8'0- is depressed;:successively to move *contactor switch arms I90 from contactwith the bus "58. -As best shown in Fig. 3, the key I80 is so mounted that the player may conveniently rest the ends of his fingers upon the lower part I92 of the top of the casing I93, while the palm of the hand is rested upon the key I80 and the wrist or forearm rests upon the elevated portion ISA of the top of the casing. By utilizing this mechanical structure for successively opening and closing the switches for the resistors RITE, the player has a very accurate and sensitive control of the dynamic output of the instrument. For purposes of comfort and to avoid fatigue the springs l8fl should be relatively light so that a minimum amount of energy is required for the operation of the key. Inasmuch as the fingers and wrist or forearm of the player are adequately supported it will be clear that the movement of the key H80 will be controllable with a high degree of alacrity so that musically interesting intensity envelopes may be imparted to successive notes in the musical composition being rendered.

The output of the pentodes I641, 165 is resistance capacity coupled to power amplifying pentodes I96, 19'! and the output of the latter coupled by a transformer 198 to a speaker 200.

It has been previously pointed out that the attack and decay portions of the tonal envelopes produced due to the changes in grid bias on triodes I50, I! as a result of depression of one of the keys and connection of the conductor Hill (Fig. lb) to ground produces very rapid attack and decay characteristics. These attack and decay rates correspond to the most rapid attack and decay which would ever be conceivably useful in the musical rendition. As explained before, this is carried out in a transientless manner devoid of any electrical clicks or thumps. Whenever a slow attack or decay is desired, as for instance, to produce an attack of a slowly bowed string or the decay of a pianolike tone, the key l8!) is operated simultaneously with the depression of the appropriate playing key 0 to B (Fig. 1c). To produce a slow decay the playing key will be held down and the dynamic volumie control key I80 gradually released.

Operation of the oscillator The Wien bridge oscillator shown in Fig. 1c is of well known type in its general circuit arrangement but, as modified for use in a musical instrument, there are a number of novel features associated therewith. In tuning an oscillator of this type successively to different frequencies, by varying a pair of resistors or a pair of capacitors in the conventional manner it is found that undesirable transients may be produced.-

In using the means disclosed in this application for tuning the oscillator, novel and musically interesting eifects are obtained because the tramsient produced by the oscillator when successive keys are played in a legato manner is of undiminished amplitude, that is, the oscillator never ceases oscillation. In addition the oscillator generates an intermediate frequency for each pair of legato notes that are played. For instance, when playing from a C key to an E key in a legato manner an intermediate frequency will be generated upon the depression of the E key, and the pitch of such intermediate tone will be approximately that of the intermediate D note. The sounding of this D note is very pleasing to the ear. In a musical sense it is perceived as a form of smooth glissando between C, D and E. To accomplish this result it is necessary that the oscillator shall not cease oscillating, and, in addition, shall successively generate two discreet frequencies as the second of a, pair of playing keys is depressed in a legato manner.

By reference to Fig. la it will be seen that when a plurality of playing keys are simultaneously depressed, the resistors R42 associated with keys below the highest depressed key are not effective in the tuning circuit. Similarly, it will be noted that upon closure of two key switches 6 I, the switch of the lower key does not have any effect in the tuning circuit since such lower resistances are efiectively connected to ground. Therefore, when two or more keys are simultaneously depressed the highest of such depressed keys will determine the steady state frequency of oscillation. However, when two keys are successively depressed in a legato manner (assuming the last depressed key is higher than the first depressed key) there will be a certain time interval during which both switches respectively associated with these two keys are closed, while only the switch 5| associated with the lower of the depressed keys is closed. During this limited time interval, the oscillator bridge circuit will be unbalanced and the frequency at which it oscillates will be intermediate the frequencies of the notes of the two depressed keys. It is also apparent that the oscillator cannot possibly stop oscillating during this interval because the impedance between the plate BI and the grid 39 has been reduced from that value which corresponds to the balanced bridge condition. Therefore, the oscillator departs in operation from the usual concept of the Wien bridge oscillator and becomes a form of multivibrator in which the new frequency is determined by a large number of parameters. However, in this condition of successive feedback energization, the frequency of oscillation will always lie approximately midway between those of the two depressed keys when the intervals are relatively small, as is usual in music. If an oscilloscope were connected to the plate 3| it would be observed thatthe oscillator never ceases oscillation when the above described tuning sequence is employed. Thus the transient contains very little low frequency, its energy being concentrated mainly at the frequencies corresponding to the first of said keys, the frequencies of the interval between the two depressed keys,

and, as the steady state is reached, the frequency of the second depressed key. There is no opportunity for a low frequency thump which might occur, for instance, if the switches 60, 6| were operated in the reverse sequence. In the latter case an undesirable thump would occur because the feedback from the plate 31 to the grid 39 would be insufficient during the time that both switches 60 and only one of the switches 6| are closed. The oscillator will likewise be tuned to an intermediate frequency when notes are played in a legato manner down the scale as well as up the scale.

The switches 62 and the circuit elements associated therewith are provided to enable the player to obtain twice as many tones as playing keys, the arrangement being such that whenever two adjacent semitone keys are simultaneously depressed both capacitors C19 and C?! will be connected in the circuit between grid 39 and ground. Thus the reactance of the circuit including these capacitors is doubled when both keys are depressed. The values of C10 and CH are such that this change in reactance in this circuit will be sufficient to decrease the frequency of? oscillation by onezaquarter of a; full tone-:ina

ciesxofrthe.notesr-C andCt and, as soon as the key- C; is released, the; oscillator will generate thefrequencyof: the note '-C#. Itwill thus be seen that the-number of I discrete frequencies avail-- able-130313116; player of-sthe instrument is-substantially twicethe numberotkeys. Since a quartertonesinterval .is a relatively-slight pitch change, ifftthe player will: playthewchromatic scale in the customary-legato manner, the musical effect'will beithatof. a smooth glissando: Thequarter-tone steps-areso small that when-th-eglissando is.

takenxata; musical; rate, the ear is unable to resolve: the effect into" its- 'disc'rete quarter-tonemally. operating. at its lowest. frequency but. no

sound. is heard-from. the-soeaker because the control switches. 53 are-not closed... When switch 202isopen, itwi-ll :beseen that. thereis no energy feedbachconrrection.betweentheplate 3-! and the grid. 39:. Therefore, there .is..no..energy feedback and-,ino oscillations. occur... When any playing keyistdepressed, the. oscillator must start from zero frequency. and arrive atthe desired frequencyof: steady-oscillation The rate at which it..arri.vesv .is controlled by .the. thermo-resistan-ce properties: ot the. thermistor 22. When. this thermistonisin the. form of a 6- watt 115. volt tungsten..incandescent lamp, the time required forthetoscillator to. reach. its steady state frequency may be approximately- 50 milliseconds. When a .playinakeyds depressed. the amplifying andoutput system will be effective to transmit the. tone. signal during atxleasta portionof this. 50 millisecond-interval. Ordinarily the listener will'be aware of the rise in freouency during approximately 40 of this 50. millisecond time in-.- terval.'. The effect produced is comparable to that of some mechanical musical instruments, such as the trumpet and saxophone. key is. de'pressed repeatedly withrapiditythe os-' cillator'maynever attain the final steady frequency correspondingito the actuated key, but will always be in the transient condition of changingdts frequency, increasing in frequency while the'switches 60,6! are closed and decreasing in-frequency'while the switches-'60, 6! are o en.

Similarly, many novel" and entertaining efiects maybe produced by playing a melody rapidly int-he" form ofshort'staccato notes. Under these circumstances; the oscillator may be in the condition' of" changingits" frequency most of the tiniwand only attain its steady 'state'when a note i's acc'ented by holdinaitdepressed for50 milli seconds. vidihg'an entertaining "variationin contrast to the normal organlike tones;

It" will be understood that an oscillatorof the when bridge type such as disclosed hereimmay be tuned by simultaneously changing the ca pacitance of-th'e two regenerative feedback circuits or simultaneously;changing' the resistances i'nthese-twd'circuitss 'I'liis will be evident from The glissandothatiis ob For instance, if a;

This-'effectis'highly desirable as pro-- 10 a consideration ofthe formula for: the frequency of oscillation of awell balanced and properly def-- signedoscillatorwhich is:

in which R1 and C1 are the total resistance and capacitanceof the series. feedback circuit/and R2- and C2 are thetota]. resistance and capacitance of the shunt feedback circuit. Thusin Fig.. 1athe resistors Bil-and R54-could bereplaced-by capacitorsif the CapacitorsC4-6, C41 and C50, C52 werereplaced.byresistors. Under these circumstances .thercapacitors C'llland- C1! in the quarter tone scale would have resistors of suitable values substituted therefor, and. the capacitors C82.and C84 .of the vibratomechanism would l kewise be replaced by resistors.. If these capacitor and resistors are thus interchanged, the relationship of the keyboard shown in Fig. la withrespect to the circuitswould have to vbe reversed, that is, the

lowest key wouldwoperate the switches 50 to 63- at theright hand endof thev diagram and the highest key would: operate the switches 60 to 53 at thelowermost. end ot the diagram, etc. Un er these. conditions-,the instrumentwould operate to. select the frequency corresponding to. the lower. or lowest .of twov or. more depressed keys.- The sequenceotoperationof theswitches 00: to. 63 would besthe same as heretoforedescribed.

Theoscillator shown in Fig. la-is of well known construction and the values-ofthe various componentsiwill thereforeibeknown or readily avail able to thoseskilled in the art. However representative values may be given, assuming the pentodes l0 and I I are of the 6V6 type.

The total resistance of theseries of R42 resistorsmay be approximately 50,000 ohms, and similarly, the total resistance of the series R54 resistors may likewise be 50,000 ohms. The resistor R42 which is connected to the conductor R44 may have a resistance in the order of 6,250

ohms'whereasthe-next adjacent resistor R42 may have a'va1ue 6% of that of the highest resistor R42; each resistor R42 having a value of about 6 of the-total resistance of the preceding series of resistors R42. The values of R54 may be com' puted in a'similar manner; 0

The operation'of the various components and sections 'of'the instrument have'been included with the detailed description thereof. eral, the instrument is designed for use as an orchestral instrument. Normally, the player will manipulate the playin key with his right hand and operate the dynamic volume control key with his-left hand. In most usesof the instrument the player will play legato-wise on thekey board and appropriate phrasin for both legato and non-legatoplaying wilI be'obtained by the-- In gendepression of the dynamic control key I80. For rapid staccato playing however, the player will reverse the operation and maintain his left hand control stationary while playing the right hand pitch determining keys in a detached non-legato manner.

The volume adjustment resistor RI 66 will usually be adjusted initially to suit the output of the instrument to the size and acoustic characteristics of the room in which the instrument is to be played.

Due to the possibility of selecting one or more of three different tone families by the selective operation of switches H2, H3 and H4 and the possibility of further modifying the tone qualities by operation of switches I46, the range in variation of tone qualities available is very great. These quality controls are disclosed in greater detail and are claimed in my copending application Serial No. 87,913, filed April 16, 1949, and the apparatus shown particularly in Figs. 2, 3, and 4 is disclosed and claimed in m copending application Serial No. 169,891, filed June 23, 1950.

While I have shown and described a particular embodiment of the invention, it will be apparent to those skilled in the art that nu.- merous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by substantially the same or equivalent means.

I claim:

1. In an electrical musical instrument having a group of playing keys, the combination of a Wien bridge oscillator having a series feedback circuit and a shunt feedback circuit, each of said circuits including resistances determinative of the frequency of oscillation; means operated by the playing keys effectively to vary the values of the resistances in both of said circuits; a pair of capacitors, switches operable by alternate playing keys to connect one of said capacitors in the shunt circuit; and switches operated by the intermediate playing keys to connect the other of the capacitors in the shunt circuit, said capacitors having such values that when two adjacent keys are depressed at the same time both of said capacitors will be effective in the shunt circuit and will cause the oscillator to operate at a frequency intermediate the frequencies at which it would oscillate upon the separate depression of said adjacent keys.

2. In an electrical musical instrument having a group of playing keys, the combination of a frequency generator of the Wien bridge type having a series feedback circuit and a shunt feedback circuit respectively provided with adjustable resistances, the values of which determine the frequency of oscillationof the oscillator; a plurality of switches operated by each of the playing keys, said switches being effective successively upon ascending the musical scale to decrease the effective values of corresponding tuning resistances in each of said circuits; and means associated with said switches and keys effective upon 12 shunt circuit prior to changing the resistance in the series circuit.

3. In an electrical musical instrument having a group of playing keys, the combination of a frequency generator of the Wien bridge type having a series feedback circuit and a shunt feedback circuit respectively provided with tuning impedances, the values of which determine the frequency of oscillation of the oscillator; a plurality of switches operated by each of the playing keys, said switches being effective successively upon ascending the musical scale to decrease the effective values of corresponding tuning impedances in each of said circuits; and means associated with said switches'and keys effective upon depression of a key to cause a change in the impedance in the series circuit prior to a change in the impedance of the shunt circuit, and upon release of a key to change the impedance in the shunt circuit prior to changing the impedance in the series circuit.

4. In an electrical musical instrument having a group of playing keys, the combination of a Wien bridge oscillator having a series feedback circuit and a shunt feedback circuit, each of said circuits including resistive and capacitative impedances determinative of the frequency of oscillation, means operated by the playing keys effectively to vary the values of the impedances of one character in both of said circuits; a pair of impedances of the other character, switches operable by alternate playing keys to connect one of said last-named impedances in the shunt circuits; and switches operated by the intermediate keys to connect the other of said last-named impedances in the shunt circuit, said last-named impedances having such values that when two adjacent keys are depressed at the same time both of said impedances will be effective in the shunt circuit and will cause the oscillator to operate at a frequency intermediate the frequencies at which it would oscillate upon the separate depression of said adjacent keys.

5. In an electrical musical instrument having a group of playing keys, the combination of a Wien bridge oscillator having a series feedback circuit and a shunt feedback circuit, each of said circuits including resistances determinative of the frequency of oscillation; means operated by the playing keys effectively to vary the values of the resistances in both of said circuits; a pair of capacitors of equal value; switches operable by. alternate playing keys to connect one of said capacitors in the shunt circuit; and switches. operated by the intermediate playing keys to connect the other of the capacitors in the shunt circuit; said capacitors having such values that when two adjacent keys are depressed at the same time both of said capacitors will be effective in the shunt circuit and will cause the oscillator to operate at a frequency intermediate thefrequencies at which it would oscillate upon the separate depression of said adjacent keys, whereby upon playing a chromatic scale in a legato manner the oscillator will successively generate frequencies-at quarter-tone intervals.

6. In an electrical musical instrument having a group of playing keys, the combination of a frequency generator of the Wien bridge type having a series feedback circuit and a shunt feedback circuit respectively provided with ad-' justable tuning resistances, the values, of which determine the frequency of oscillation of the 05-,

cillator; a plurality of switches operated by each anagram of said keys; saidswitches being effective successively upon ascending the-musical scaleutoide. crcaseatheeeifective values, of.- corresponding tun:- ing; resistances in each of said circuits means associated, with said switches; ranch: keys; effective upon depression of a key to-cause a change in the: resistance in the seriescircuit prior to a change, in the resistance of thershunt circuit,, and upon releasez of a key to changethe resistance in the shunt circuit prior to changing the impedance in the series circuit; a vibrato capacitor; and cyclically operating means alternately to connect and disconnect the vibrato capacitor in the shunt feedback circuit at a rate in the order of 7 cycles per second, thereby to raise and lower the frequency of the oscillator in a manner to produce a vibrato effect.

7. In an electrical musical instrument having a group of playing keys, the combination of a frequency generator of the Wien bridge type having a series feedback circuit and a shunt feedback circuit respectively provided with adjustable tuning resistances, the values of which determine the frequency of oscillation of the oscillator; a plurality of switches operated by each of the playing keys, said switches being effective successively upon ascending the musical scale to decrease the effective values of the tuning resistances in each of said circuits; means associated with said switches and keys effective upon depression of a key to cause a change in the resistance in the series circuit prior to a change in the resistance of the shunt circuit, and upon release of a key to change the resistance in the shunt circuit prior to changing the resistance in the series circuit; and a switch operable, when all the key operated switches are open, upon closure to connect the maximum tuning resistance in the series feedback circuit and upon opening to open the series feed-back circuit.

8. In an electrical musical instrument having a group of playing keys, the combination of a frequency generator of the Wien bridge type having a series feedback circuit and a shunt feedback circuit respectively provided with adjustable tun-, ing impedances, the values of which determine the frequency of oscillation of the oscillator; a plurality of switches controlled by each of the playing keys, said switches being effective successively upon ascending the musical scale to change the effective values of corresponding tuning impedances in each of said circuits; and means associated with said switches and keys effective upon depression of a key to cause a change in the impedance in the series circuit and thereafter a change in the impedance of the shunt circuit, and upon release of a key to cause a change in the impedance in the shunt circuit and thereafter a change in the impedance in the series circuit.

9. Tuning means for a Wien bridge oscillator having a pair of electron discharge devices provided with two frequency determining circuits, each of said circuits including resistance and capacitance impedance elements, and key operated meansoperative to change the effective values of corresponding impedances in both of said circuits in a predetermined sequence, one after the other.

10. In an electrical musical instrument having a tone signal generating system including a bridge type oscillator having shunt and series regenerative feedback circuits the impedances of which determine its frequency of oscillation, the

combination of azpl-urality off: playing-" keys; a

pair OfjiSWlllOhES operated:sequentially, byea'ch of said keys, and means -::controlled by: said switchesr to change corresponding tuning impedances of each of the. circuits,".the: first. operated switch being-inthe: series: feedback circuit;

11. Tuningmeans for aWien"bridgeoscillator having a pair of i electron discharge devices provided with two" frequencydetermining circuits, each ofJsa-id circuits including resistance andcapacitance-impedance elements, and key operated means operative to change the effective values of the resistanceimpedance elements in both :of said 'circuits'in a predetermined sequence, one after the other.

12. In an electrical musical instrument having an oscillator and a plurality of playing keys, an oscillator tuning circuit having means for changing its impedance in accordance with the operation of the keys to generate the frequencies of the semitone musical scale, and additional tuning means rendered effective upon the concurrent depression of two adjacent keys to change the frequency of oscillation of the oscillator to a frequency intermediate the frequencies to which the oscillator would be tuned by the separate depression of the two adjacent keys.

13. In an electrical musical instrument having an oscillator and a plurality of playing keys, an oscillator tuning circuit having means for changing its impedance in accordance with the operation of the keys to generate the frequencies of the semitone musical scale, and additional tuning means to change the frequency of oscillation of the oscillator to frequencies intermediate the semitone frequencies of the musical scale upon concurrent depression of the keys for adjacent semi-tones.

14. In an electrical musical instrument having a plurality of playing keys, an oscillator for determining the frequency of the electrical tone signals produced, said oscillator having a tuning circuit including impedances of different character, means operated by the playing keys progressively to change the effective values of impedances of one character so as to tune the oscillator to the frequencies of the semitone intervals of the temp-cred musical scale upon successive depression of the keys, and additonal tuning impedances of different character rendered effective by the keys to change the frequency of oscillation of the oscillator by a quarter-tone interval when two adjacent keys are depressed concurrently.

15. In an electrical musical instrument having a plurality of playing keys, and an oscillator for determining the frequency of the electrical tone signals produced, said oscillator having a tuning circuit including resistive and capacitative impedances, means operated by the playing keys progressively to change the effective values of impedances of one character so as to tune the oscillator to the frequencies of the semitone intervals of the tempered musical scale upon' successive depression of the keys, and additional tuning impedances of the other character rendered effective by the keys to change the frequency of oscillation of the oscillator by a quarter-tone interval when two adjacent keys are depressed concurrently.

16. In an electrical musical instrument having a plurality of playing keys, an oscillator for determining the frequency of the electrical tone signals produced, said oscillator having a tuning 15 circuit including impedances, means operated by the playing keys progressively to change the effective values of the impedances so as to tune the oscillator to the frequencies of the semi-tone intervals of the tempered musical scale upon successive depression of the keys, and additional tuning impedances rendered effective by the keys to change the frequency of oscillation of the oscillator by a quarter tone interval when two adjacent keys are depressed concurrently.

JOHN M. HANERT.

REFERENCES CITED The following references are of record in the file of this patent;

Number UNITED STATES PATENTS Name Date Hammond June 6, 1939 Scott Sept. 19, 1939 Hanert Sept. 2, 1941 Hewlett Jan. 6, 1942 Hanert Mar. 17, 1942 Hanert Nov. 10, 1942 Artzt June 29, 1948 

